I personally find the Olympus 40-150mm sharper than the Panasonic 45-200mm on my E-PM1.
It's also a lot smaller and lighter.
Also I have had no IBIS issues using either lens (I had OIS off on the Panny).

When I'm shooting a long tele, I'm usually shooting in daylight, and shutter speeds are not an issue for me, so I chose the 40-150 for size.

I tested the 150 vs. the 200. I found the 200 as sharp if not sharper than the 40-150 at most focal lengths BUT the 200 softens at 200. If you shoot automatically at the end of the range, then you'll be shooting at 200, and it will be softer than the 150. If you shoot purposely at 150, you'll have just as good a lens. Also, the 45-200 stops down at a slower right, so it had a slightly brighter aperture at equivalent focal lengths than the 40-150. I think the 45-200 also had slightly better color and contrast, though neither lenses will win prizes here.

For me, I test the IBIS on the 40-150 and the OIS on the 45-200 in good light. Oddly, the BOTH showed issues with IS at good shutter speeds, but the 45-200 has a handy external IS switch, so you can turn it on only when needed. If IS is really important to you, then the 45-200 is really the choice. For compactness and if IS is not important, then I prefer the 40-150. Some of the other factors above may or may not sway you one way or the other.

I had the 45-200, it's a sharp lens as long as it's used in good light. It focuses pretty quick on the E-PM1 and it's not that big if you're used to Nikkor zooms. This was all shot with the E-PL2. Personally I prefer the 100-300. Which is still pretty sharp at 300mm! :smile:

I really like the 45-200. I found that I really needed to get the hang of it but I think it is a bit nicer than the 40-150. I prefer the greater reach. I think the 40-150 is better size-wise than the 45-200.

Here are the test shots I used when deciding on which lens to keep.
Very unscientific I know, but it was good enough at the time.
I was mainly looking for sharpness and accurate focus.
Both lenses where shot on an E-PM1 at 150mm (well the Panny was at 151mm according to the EXIF) and focused on the center of the text in the middle bottle.
OOC jpgs.

Here are the test shots I used when deciding on which lens to keep.
Very unscientific I know, but it was good enough at the time.
I was mainly looking for sharpness and accurate focus.
Both lenses where shot on an E-PM1 at 150mm (well the Panny was at 151mm according to the EXIF) and focused on the center of the text in the middle bottle.
OOC jpgs.